The purpose of this research is to investigate whether dose of haloperidol and blood levels of haloperidol are important factors in predicting prevention of relapse in schizophrenic patients, who are maintained on outpatient neuroleptic maintenance therapy. It will also investigate the ability of brain morphological abnormalities as were revealed by CAT Scans and neuropsychological tests to predict relapse in schizophrenic outpatients and/or dosage and blood level requirements during maintenance neuroleptic therapy of schizophrenic outpatients. One hundred ninety five patients will be randomly assigned to one of three different doses of haloperidol, and multiple ratings of psychopathology and relapse or prodromal worsening will be monitored over a period of 18 months. Blod levels of haloperidol will be assessed by both gas liquid chromatography and radioreceptor assay. One of the main aims of the study is to compare the efficacy of GLC and RR assays in prediction of clinical and response or prevention of relapse in the schizophrenic outpatients treated with neuroleptics. A subset of patients will receive CT Scans on which multiple quantitative measurements of brain ventricles, brain density, and brain atrophy will be performed. These will be correlated with psychopathology scores during maintenance treatment. This project will help to answer important questions regarding the clinical treatment of schizophrenics who require maintenance neuroleptic therapy. It will provide answers to such questions as: (1) Is there a minimum dose of neuroleptics which is effective in the treatment of schizophrenic outpatients, and do high doses not increase drug efficacy?; (2) Do blood levels predict clinical response in schizophrenic outpatients maintained on neuroleptics, and is there a statistically significant blood level vs. clinical response relationship for the neuroleptic haloperidol?; (3) Do morphological abnormalities help predict dosage requirements or relapse rates in schizophrenic outpatients, and can they be used to specify which schizophrenic patients will benefit most or benefit least from maintenance neuroleptic outpatient therapy.